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Discussion Starter · #1 ·
Hey fellas, as everybody knows the birds chassis is rather flimsy. Subframe connectors and other braces greatly increase the strength of this car but it still ain’t enough.

In comes seam stitch welding, which is pretty much where you weld 1-3” sections of the entire body, everywhere there is spot welds In order to help the body retain in shape. The problem with that is, it very time consuming, adds some weight and if your not a welder the price to get it done is REDICULOUS.

So what I’ve been pondering is Sean sealants.


I recently came across a thread where the guys uses this in the engine bay to stiffen it up without welding.


Here the guys sands it down to bare metal and applies the sealant all up in the seams.

Does anybody here have any experience with this? He claims to have done it on his buddies crz with great results WITHOUT having to sand down any paint. I’m really considering this option due to the simplicity. I was thinking starting in the engine bay and down the road doing the underchassis/interior/rear.

I’m not sure if this belongs here so please move if needed mods.

Hoping to start a good convo on the the structural integrity of our cars and ways to improve it!
 

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Yeah I used to work on the body seam sealer line in the passenger paint department at NUMMI - we built Toyotas and Pontiac vehicles before it shut down in 2009 and Tesla took over.

The seam sealer was applied for waterproofing and to prevent corrosion. The sealer was applied over the corrosion inhibitor dip over bare metal before it went to primer / paint. After the sealer is applied over the seam, a skiving tool was used to push the sealer into the space between the seams and everything else was laid flat.

We were told that this provided additional strength / ridgity along with all of the rest of the tar mats that were applied to the floorboards and trunk space ( for those who remove the tar mats for weight reduction ).

I would avoid any kind of non hardening pliable seam sealers, they are for waterproofing and corrosion resistance.

One part seam sealer is usually applied to bare metal, two part sealers are applied over a corrosion resistant coating. Some sealers need to be baked in an oven or have heat applied to cure the sealer. The sealer you listed is more of a panel bonding adhesive ( it has glass beads to ensure proper spacing when panels are clamped together ) .. I would look into something more like the structural sealer variety.
 

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Discussion Starter · #4 ·
Yeah I used to work on the body seam sealer line in the passenger paint department at NUMMI - we built Toyotas and Pontiac vehicles before it shut down in 2009 and Tesla took over.

The seam sealer was applied for waterproofing and to prevent corrosion. The sealer was applied over the corrosion inhibitor dip over bare metal before it went to primer / paint. After the sealer is applied over the seam, a skiving tool was used to push the sealer into the space between the seams and everything else was laid flat.

We were told that this provided additional strength / ridgity along with all of the rest of the tar mats that were applied to the floorboards and trunk space ( for those who remove the tar mats for weight reduction ).

I would avoid any kind of non hardening pliable seam sealers, they are for waterproofing and corrosion resistance.

One part seam sealer is usually applied to bare metal, two part sealers are applied over a corrosion resistant coating. Some sealers need to be baked in an oven or have heat applied to cure the sealer. The sealer you listed is more of a panel bonding adhesive ( it has glass beads to ensure proper spacing when panels are clamped together ) .. I would look into something more like the structural sealer variety.
Sensei! This is great info right here. I’m barely starting to wrap my head around the actual structure of a car. stuff like this is what separates older tech to more modern structures.


I found this, from 3m aswell and it says structural adhesive.

I’m pretty new at the concepts so it’s a learning process. The end goal is making the bird a lot tighter through methods the engineers would make.
 

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Discussion Starter · #5 ·


If this is a stock 240sx and it has the seam sealer everywhere, I can only imagine the same method on the bird would help substantially. It literally has none haha
 

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If this is a stock 240sx and it has the seam sealer everywhere, I can only imagine the same method on the bird would help substantially. It literally has none haha
I can see where the sealer has been applied to that 240 .. it's primary purpose inside the seams is to prevent rust / corrosion. There isn't much here, they were very sparing on this engine bay.



Here is fhe Tbird door. The seam sealer is applied along the bottom as indicated by the slight ridge leading to the corner .. from there brush strokes are visible where the factory brushed the trailing edge of the sealer for two reasons - to clean up the appearance, and to push the sealer into the corner. The edge of this door has no sealer. Excess sealer globs are present on the top edge near the door panel opening where the panel and plastic normally covers the inner door.

I would have been written up for this Tbird application - the bead is extremely thin, it may have been applied very quickly and the ridge on the top edge tells me that the sealer gun used has a damaged applicator tip.



This is what you will find on a newer vehicle. The sealer has been applied directly over the seam on the door edge - typically the same width sealer bead is applied to the bottom of the door seam - it doesn't look like much is evident here because the rubber weatherstripping covers the bead but it is in fact there as well. This looks like the factory used a skiving tool to clean up the corner / push the sealer into the seam. A little high and far back if you ask me - when I skived the corners on the Toyotas, we only pushed about an inch of the corner so as not to end up with excess sealer in my cup ( most people simply wipe the excess into the interior, which is where you will find random gobs of sealer that don't seem to have any purpose - like on the Tbird door ) .. sort of like those little gobs on the frame rail towards the front end on that 240, it's extra sealer that was not cleaned up. We had quality control inspections heavily on the Toyotas that ran down the assembly line .. almost no QC on the GM vehicles ( except for the leak test performed after final assembly where the car goes through a monsoon shower before it goes to Final QC )

So .. just to clarify, seam sealer applied and skived directly into the seam with excess cleaned up is for corrosion resistance and waterproofing. Wide beads of seam sealer applied directly over the seam provide more strength.

Most of the sealer inside our Toyota cars was applied by robots ( in this case about 20x $1 million dollar Kawasaki robots on the sealer line after De-jig from the chemical corrosion dip ) .. the robots applied about a 6 inch wide layer of sealer throughout the interior and engine compartment and we got away from laying down tar mats in the interior in favor of robot applied layers of sealer. Also serves as a sound deadener.
 

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Discussion Starter · #7 ·
I can see where the sealer has been applied to that 240 .. it's primary purpose inside the seams is to prevent rust / corrosion. There isn't much here, they were very sparing on this engine bay.

View attachment 49839

Here is fhe Tbird door. The seam sealer is applied along the bottom as indicated by the slight ridge leading to the corner .. from there brush strokes are visible where the factory brushed the trailing edge of the sealer for two reasons - to clean up the appearance, and to push the sealer into the corner. The edge of this door has no sealer. Excess sealer globs are present on the top edge near the door panel opening where the panel and plastic normally covers the inner door.

I would have been written up for this Tbird application - the bead is extremely thin, it may have been applied very quickly and the ridge on the top edge tells me that the sealer gun used has a damaged applicator tip.

View attachment 49840

This is what you will find on a newer vehicle. The sealer has been applied directly over the seam on the door edge - typically the same width sealer bead is applied to the bottom of the door seam - it doesn't look like much is evident here because the rubber weatherstripping covers the bead but it is in fact there as well. This looks like the factory used a skiving tool to clean up the corner / push the sealer into the seam. A little high and far back if you ask me - when I skived the corners on the Toyotas, we only pushed about an inch of the corner so as not to end up with excess sealer in my cup ( most people simply wipe the excess into the interior, which is where you will find random gobs of sealer that don't seem to have any purpose - like on the Tbird door ) .. sort of like those little gobs on the frame rail towards the front end on that 240, it's extra sealer that was not cleaned up. We had quality control inspections heavily on the Toyotas that ran down the assembly line .. almost no QC on the GM vehicles ( except for the leak test performed after final assembly where the car goes through a monsoon shower before it goes to Final QC )

So .. just to clarify, seam sealer applied and skived directly into the seam with excess cleaned up is for corrosion resistance and waterproofing. Wide beads of seam sealer applied directly over the seam provide more strength.

Most of the sealer inside our Toyota cars was applied by robots ( in this case about 20x $1 million dollar Kawasaki robots on the sealer line after De-jig from the chemical corrosion dip ) .. the robots applied about a 6 inch wide layer of sealer throughout the interior and engine compartment and we got away from laying down tar mats in the interior in favor of robot applied layers of sealer. Also serves as a sound deadener.
I see what your saying, so they is Seam sealant in between all the seams MAINLY to seal them off to the environment?? I see that how they protect the car from rusting out in those hard to reach places.
So if I was to apply that impact resistant sealant, I’d have to put it over the seam itself??



From these pictures, the idea is to get it on pretty much the whole front end inside the fender and the engine bay. The shock showers look like this would do wonders. Those gaps are hideous on top. I’m surprised nobody has popped welds in this area. If I were to do it, I’d put the sealant over the top of both sheet metals? In the write up of the 240 he says he would add the sealant over top and pass his finger over the seams to get the sealant inside the panels aswell.
pretty much I’d like to start at the engine bay and work inside roof/rear shelf The area underneath the rear window.
 

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Discussion Starter · #9 ·
Mark VIIIs had seam sealer applied there from the factory, in addition to some additional stitch welds along the inner and outer shock tower

Nobody pops the welds because it’s not really an issue

ive googled the mark 8 engine bays and haven’t been able to find one with sealer on the shock towers, I’m assuming the later years got it? makes me wanna hit the junkyard just to study the mark 8 differences haha

stich welding on the front towers? That’s interesting, it seems to me the marks are an overall stronger chassis. they also have those x braces behind the rear seat. my bird have all 3 braces back there and it does make a big difference.



in the future I’d like to weld some tabs like on the marks on the lower corners and make a legit x brace instead of the stamped steel pieces.




where else do you guys know of where the bird could use a lil extra help? I’ve seen jaguars have an x brace that goes on the radiator support. It grabs the ends of the frame rails uppers\lowers and stops them from, I not sure of the word but it helps well the rails str8 instead of shifting.
 

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Mark VIIIs had seam sealer applied there from the factory, in addition to some additional stitch welds along the inner and outer shock tower

Nobody pops the welds because it’s not really an issue
I don't recall seam sealer, just the stitch welds on top of the upper mounting plate fingers to inner fender.

The spot welds popped in this area on my Tbird with air suspension - which is why the Mark's had additional weld here. If / when the air suspension fails, the car rides directly on the bumps tops and puts a lot more stress on that upper mount.
 

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Maybe it isn’t seam sealer as I look closer, there’s some sort of soft rectangular pad in between the fingers and fender rails on them, it might be a Gen II thing



Here’s a ok pic of the welds, it’s harder to find pics online since the shock covers cover them, but you can see the notches on MN12s where they would go as well




@Noser7mil The El Camino is body on frame, the entire front body structure is bolted together and contains very little support structure other than the frame rails, so those literally just help keep the core support stamping from buckling and the fenders from falling off, apples and oranges. Those dinky little bolt on braces it has will do exactly nothing to a unibody structure
 

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Okay .. I dont remember that pad on the Gen 1 Mark's I have owned but then again its been at least 10 years since then. Yes the "Notch" .. I believe there are two notches on the shock mount that received the stitch weld - again this is re-inforcement for the air suspension.

I think I need to watch the video Noser is referring to before I come to any conclusions about the benefits of using seam sealer as an alternative to full seam welding. I would personally weld the seams, it might go a lot faster with an arc / stick weld than to stitch it with a MIG - I have access to multiple types of welders here. It would be more solid with some kind of fiberglass reinforced body filler over seam sealer. Even the structural sealer mentioned above is actually meant for bonding between panels before spot welding them together.
 

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Discussion Starter · #14 ·
Maybe it isn’t seam sealer as I look closer, there’s some sort of soft rectangular pad in between the fingers and fender rails on them, it might be a Gen II thing

View attachment 49850

Here’s a ok pic of the welds, it’s harder to find pics online since the shock covers cover them, but you can see the notches on MN12s where they would go as well

View attachment 49852


@Noser7mil The El Camino is body on frame, the entire front body structure is bolted together and contains very little support structure other than the frame rails, so those literally just help keep the core support stamping from buckling and the fenders from falling off, apples and oranges. Those dinky little bolt on braces it has will do exactly nothing to a unibody structure
Thank you for the pictures. You can barely see those stitch welds your talking about, is it just those 2? I always wondered why they went with a 2 piece strut tower. Every other car I see is only 1 solid piece. Here’s and engine bay shot of another mark 8 on the Facebook forum and you can clearly see those welds you pointed out. His name is Bryan young.


i see our cars are unibody chassis! That’s interesting. The new mustangs performance package also have some lil braces at the rad support aswell. They look like they grab from the frame rail to the hood latch area. I’m pretty sure it’s the same concept. I’ve been looking at how different cars improve the rigidity through various braces.



Okay .. I dont recall that pad on the Gen 1 Mark's I have owned but then again its been at least 10 years since then. Yes the "Notch" .. I believe there are two notches on the shock mount that received the stitch weld - again this is re-inforcement for the air suspension.

I think I need to watch the video Noser is referring to before I come to any conclusions about the benefits of using seam sealer as an alternative to full seam welding. I would personally weld the seams, it might go a lot faster with an arc / stick weld than to stitch it with a MIG - I have access to multiple types of welders here. It would be more solid with some kind of fiberglass reinforced body filler over seam sealer. Even the structural sealer mentioned above is actually meant for bonding between panels before spot welding them together.
That stick welding you stayed to me makes the most sense to seal up all those seams on the shock tower. I have a trusty muffler shop that might be able to stitch up mine just not sure if he can handle this job since it’s not an exhaust part.
 

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Discussion Starter · #15 ·

Here is and s197 rear seat and besides the x brace, the other thing that pops up at me is that center brace that goes up to just underneath the X. I wonder if I can go to a junkyard and grab that piece to retrofit onto the bird. It won’t be too much weight anyways.
 

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Discussion Starter · #16 ·

This is also a brace for the s197. The boss 302 has one similar from the factory. It ties the front of the Kmember to the rad support.
 

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i see our cars are unibody chassis! That’s interesting. The new mustangs performance package also have some lil braces at the rad support aswell. They look like they grab from the frame rail to the hood latch area. I’m pretty sure it’s the same concept. I’ve been looking at how different cars improve the rigidity through various braces. View attachment 49858
View attachment 49859
Those aren't braces, at least not in the prevent chassis flex sort of kind, all those are are supports for the upper core support/header panel which is a bolt on affair on S550 mustangs, they're just there to prevent it drooping down in the middle. In that sense they're not all that dissimilar in purpose to the ones used on the El Camino which also uses a bolt together front structure. That's not very pertinent to MN12s though








On that note also unlike MN12s the lower radiator support is also bolted in on new Mustangs, and the design is quite a bit different, it's thin flexible sheetmetal on ours, you can literally hand bend it back to shape if you damaged it its so pliable, trying to brace it to the K member to it wont to anything - if there's movement between the two the K member and braces will simply flex the flimsy rad support.

Mustang lower radiator supports are much more robust... Now I bet you're asking yourself "if the radiator support is beefier, it must be there to stiffen the chassis, right? upgrade!" Nope :) the Radiator support is beefy on Mustangs because it doubles as the mounting points for the front sway bar. MN12s of course have those self contained within the K member itself, so there's no need for the radiator support to be any beefier than it is, and since it contains no suspension related componentry there's no conceivable benefit to bracing the two together




Very telling that Ford makes all this crap bolt on on newer Mustangs, very easy repair after they crash into crowds 😆
 

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sense to seal up all those seams on the shock tower. I have a trusty muffler shop that might be able to stitch up mine just not sure if he can handle this job since it’s not an exhaust part.
I'm sure you could buy a used ARC weld machine, angle grinder and a hood for what you would pay a couple hours labor. Spend a little time practicing and it will be way more cost effective than relying on somebody else.
 

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If you look at that hump in the middle, see that big bolt and washer?
Underneath the floor right there, is a bracket that is the mount for the body side of the single upper control arm. S197 is a 3-link rear suspension with a panhard bar.
Team Z makes a 1/4" steel bracket that replaces the factory stamped piece, and it was one of the best handling mods i made to the car.
 

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Discussion Starter · #20 ·
Those aren't braces, at least not in the prevent chassis flex sort of kind, all those are are supports for the upper core support/header panel which is a bolt on affair on S550 mustangs, they're just there to prevent it drooping down in the middle. In that sense they're not all that dissimilar in purpose to the ones used on the El Camino which also uses a bolt together front structure. That's not very pertinent to MN12s though

View attachment 49863


View attachment 49862

View attachment 49864

On that note also unlike MN12s the lower radiator support is also bolted in on new Mustangs, and the design is quite a bit different, it's thin flexible sheetmetal on ours, you can literally hand bend it back to shape if you damaged it its so pliable, trying to brace it to the K member to it wont to anything - if there's movement between the two the K member and braces will simply flex the flimsy rad support.

Mustang lower radiator supports are much more robust... Now I bet you're asking yourself "if the radiator support is beefier, it must be there to stiffen the chassis, right? upgrade!" Nope :) the Radiator support is beefy on Mustangs because it doubles as the mounting points for the front sway bar. MN12s of course have those self contained within the K member itself, so there's no need for the radiator support to be any beefier than it is, and since it contains no suspension related componentry there's no conceivable benefit to bracing the two together

View attachment 49865


Very telling that Ford makes all this crap bolt on on newer Mustangs, very easy repair after they crash into crowds 😆
Ahhh thank you for clearing that up about the braces on the s550 it always looked to me that they were there to stop the front from deforming over bumps and stuff.
also no WONDER the sway bar on the s197 is on the rad support haha. Ford did a great job on those models but like you said, looks really easy to change parts WHEN you run into a crowd haha

if you were to add some sort of rigidity to our cars where would you start?


I'm sure you could buy a used ARC weld machine, angle grinder and a hood for what you would pay a couple hours labor. Spend a little time practicing and it will be way more cost effective than relying on somebody else.
I’ve been having my eye on this specific one, checked reviews on YouTube and got nothing but great feed back, it’s a flux welder so no gas. My only problem is I don’t have a garage or something to actually weld up anything. I’d love to learn on the bird by making the rear seat braces similar to the mark 8’s.

do you have any braces on your bird?


If you look at that hump in the middle, see that big bolt and washer?
Underneath the floor right there, is a bracket that is the mount for the body side of the single upper control arm. S197 is a 3-link rear suspension with a panhard bar.
Team Z makes a 1/4" steel bracket that replaces the factory stamped piece, and it was one of the best handling mods i made to the car.
Ahhh I see! I always thought it was for strengthening that area. It looks super robust haha but I can see that bolt your speak of, I completely forgot the s197 got a bit a hard bar out back. Id like to get a mustang one day but I just love the birds interior too much, it’s so spacious!!
 
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